Convergence of electronic bands for high performance bulk thermoelectrics
TL;DR: It is demonstrated that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition, leading to an extraordinary zT value of 1.8 at about 850 kelvin.
Abstract: Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known, that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe_(1) − _(x)Se_(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.
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TL;DR: An unprecedented ZT of 2.6 ± 0.3 at 923 K is reported in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell, which highlights alternative strategies to nanostructuring for achieving high thermoelectric performance.
Abstract: The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat The efficiency of thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion Enhancements above the generally high threshold value of 25 have important implications for commercial deployment, especially for compounds free of Pb and Te Here we report an unprecedented ZT of 26 ± 03 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell This material also shows a high ZT of 23 ± 03 along the c axis but a significantly reduced ZT of 08 ± 02 along the a axis We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Gruneisen parameters, which reflect the anharmonic and anisotropic bonding We attribute the exceptionally low lattice thermal conductivity (023 ± 003 W m(-1) K(-1) at 973 K) in SnSe to the anharmonicity These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance
3,823 citations
TL;DR: It is shown that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials, and an increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoeLECTrics.
Abstract: Controlling the structure of thermoelectric materials on all length scales (atomic, nanoscale and mesoscale) relevant for phonon scattering makes it possible to increase the dimensionless figure of merit to more than two, which could allow for the recovery of a significant fraction of waste heat with which to produce electricity.
3,670 citations
TL;DR: The results indicate a new strategy and direction for high-efficiency thermoelectric materials by exploring systems where there exists a crystalline sublattice for electronic conduction surrounded by liquid-like ions.
Abstract: Advanced thermoelectric technology offers a potential for converting waste industrial heat into useful electricity, and an emission-free method for solid state cooling. Worldwide efforts to find materials with thermoelectric figure of merit, zT values significantly above unity, are frequently focused on crystalline semiconductors with low thermal conductivity. Here we report on Cu_(2−x)Se, which reaches a zT of 1.5 at 1,000 K, among the highest values for any bulk materials. Whereas the Se atoms in Cu_(2−x)Se form a rigid face-centred cubic lattice, providing a crystalline pathway for semiconducting electrons (or more precisely holes), the copper ions are highly disordered around the Se sublattice and are superionic with liquid-like mobility. This extraordinary ‘liquid-like’ behaviour of copper ions around a crystalline sublattice of Se in Cu_(2−x)Se results in an intrinsically very low lattice thermal conductivity which enables high zT in this otherwise simple semiconductor. This unusual combination of properties leads to an ideal thermoelectric material. The results indicate a new strategy and direction for high-efficiency thermoelectric materials by exploring systems where there exists a crystalline sublattice for electronic conduction surrounded by liquid-like ions.
1,609 citations
TL;DR: A record high ZTdev ∼1.34, with ZT ranging from 0.7 to 2.0 at 300 to 773 kelvin, realized in hole-doped tin selenide (SnSe) crystals, arises from the ultrahigh power factor, which comes from a high electrical conductivity and a strongly enhanced Seebeck coefficient enabled by the contribution of multiple electronic valence bands present in SnSe.
Abstract: Thermoelectric technology, harvesting electric power directly from heat, is a promising environmentally friendly means of energy savings and power generation. The thermoelectric efficiency is determined by the device dimensionless figure of merit ZT(dev), and optimizing this efficiency requires maximizing ZT values over a broad temperature range. Here, we report a record high ZT(dev) ∼1.34, with ZT ranging from 0.7 to 2.0 at 300 to 773 kelvin, realized in hole-doped tin selenide (SnSe) crystals. The exceptional performance arises from the ultrahigh power factor, which comes from a high electrical conductivity and a strongly enhanced Seebeck coefficient enabled by the contribution of multiple electronic valence bands present in SnSe. SnSe is a robust thermoelectric candidate for energy conversion applications in the low and moderate temperature range.
1,542 citations
TL;DR: This review describes the recent advances in designing high-performance bulk thermoelectric materials and highlights the decoupling of the electron and phonon transport through coherent interface, matrix/precipitate electronic bands alignment, and compositionally alloyed nanostructures.
Abstract: There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...
1,469 citations
References
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TL;DR: A new era of complex thermoelectric materials is approaching because of modern synthesis and characterization techniques, particularly for nanoscale materials, and the strategies used to improve the thermopower and reduce the thermal conductivity are reviewed.
Abstract: Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.
8,999 citations
TL;DR: Thermoelectric materials are solid-state energy converters whose combination of thermal, electrical, and semiconductor properties allows them to be used to convert waste heat into electricity or electrical power directly into cooling and heating.
Abstract: Thermoelectric materials are solid-state energy converters whose combination of thermal, electrical, and semiconducting properties allows them to be used to convert waste heat into electricity or electrical power directly into cooling and heating. These materials can be competitive with fluid-based systems, such as two-phase air-conditioning compressors or heat pumps, or used in smaller-scale applications such as in automobile seats, night-vision systems, and electrical-enclosure cooling. More widespread use of thermoelectrics requires not only improving the intrinsic energy-conversion efficiency of the materials but also implementing recent advancements in system architecture. These principles are illustrated with several proven and potential applications of thermoelectrics.
4,700 citations
14 Jul 1995
TL;DR: In this article, Rowe et al. proposed a method for reducing the thermal conductivity of a thermoelectric generator by reducing the carrier concentration of the generator, which was shown to improve the generator's performance.
Abstract: Introduction, D.M. Rowe General Principles and Theoretical Considerations Thermoelectric Phenomena, D.D. Pollock Coversion Efficiency and Figure-of-Merit, H.J. Goldsmid Thermoelectric Transport Theory, C.M. Bhandari Optimization of Carrier Concentration, C.M. Bhandari and D.M. Rowe Minimizing the Thermal Conductivity, C.M. Bhandari Selective Carrier Scattering in Thermoelectric Materials, Y.I. Ravich Thermomagnetic Phenomena, H.J. Goldsmid Material Preparation Preparation of Thermoelectric Materials from Melts, A. Borshchevsky Powder Metallurgy Techniques, A.N. Scoville PIES Method of Preparing Bismuth Alloys, T. Ohta and T. Kajikawa Preparation of Thermoelectric Materials by Mechanical Alloying, B.A. Cook, J.L. Harringa, and S.H. Han Preparation of Thermoelectric Films, K. Matsubara, T. Koyanagi, K. Nagao, and K. Kishimoto Measurement of Thermoelectric Properties Calculation of Peltier Device Performance, R.J. Buist Measurements of Electrical Properties, I.A. Nishida Measurement of Thermal Properties, R. Taylor Z-Meters, H.H. Woodbury, L.M. Levinson, and S. Lewandowski Methodology for Testing Thermoelectric Materials and Devices, R.J. Buist Thermoelectric Materials Bismuth Telluride, Antimony Telluride, and Their Solid Solutions, H. Scherrer and S. Scherrer Valence Band Structure and the Thermoelectric Figure-of-Merit of (Bi1-xSbx)Te3 Crystals, M. Stordeur Lead Telluride and Its Alloys, V. Fano Properties of the General Tags System, E.A. Skrabek and D.S. Trimmer Thermoelectric Properties of Silicides, C.B. Vining Polycrystalline Iron Disilicide as a Thermoelectric Generator Material, U. Birkholz, E. Gross, and U. Stohrer Thermoelectric Properties of Anisotropic MnSi1.75 , V.K. Zaitsev Low Carrier Mobility Materials for Thermoelectric Applications, V.K. Zaitsev, S.A. Ktitorov, and M.I. Federov Semimetals as Materials for Thermoelectric Generators, M.I. Fedorov and V.K. Zaitsev Silicon Germanium, C.B. Vining Rare Earth Compounds, B.J. Beaudry and K.A. Gschneidner, Jr. Thermoelectric Properties of High-Temperature Superconductors, M. Cassart and J.-P. Issi Boron Carbides, T.L. Aselage and D. Emin Thermoelectric Properties of Metallic Materials, A.T. Burkov and M.V. Vedernikov Neutron Irradiation Damage in SiGe Alloys, J.W. Vandersande New Materials and Performance Limits for Thermoelectric Cooling, G.A. Slack Thermoelectric Generation Miniature Semiconductor Thermoelectric Devices, D.M. Rowe Commercially Available Generators, A.G. McNaughton Modular RTG Technology, R.F. Hartman Peltier Devices as Generators, G. Min and D.M. Rowe Calculations of Generator Performance, M.H. Cobble Generator Applications Terrestrial Applications of Thermoelectric Generators, W.C. Hall Space Applications, G.L. Bennett SP-100 Space Subsystems, J.F. Mondt Safety Aspects of Thermoelectrics in Space, G.L. Bennett Low-Temperature Heat Conversion, K. Matsuura and D.M. Rowe Thermoelectric Refrigeration Introduction, H.J. Goldsmid Module Design and Fabrication, R. Marlow and E. Burke Cooling Thermoelements with Superconducting Leg, M.V. Vedernikov and V.L. Kuznetsov Applications of Thermoelectric Cooling Introduction, H.J. Goldsmid Commercial Peltier Modules, K.-I. Uemura Thermoelectrically Cooled Radiation Detectors, L.I. Anatychuk Reliability of Peltier Coolers in Fiber-Optic Laser Packages, R.M. Redstall and R. Studd Laboratory Equipment, K.-I. Uemura Large-Scale Cooling: Integrated Thermoelectric Element Technology, J.G. Stockholm Medium-Scale Cooling: Thermoelectric Module Technology, J.G. Stockholm Modeling of Thermoelectric Cooling Systems, J.G. Stockholm
4,192 citations
TL;DR: In this article, the ability to achieve a simultaneous increase in the power factor and a decrease in the thermal conductivity of the same nanocomposite sample and for transport in the same direction is discussed.
Abstract: Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena found both in bulk samples containing nanoscale constituents and in nanoscale samples themselves. Prior theoretical and experimental proof-of-principle studies on quantum-well superlattice and quantum-wire samples have now evolved into studies on bulk samples containing nanostructured constituents prepared by chemical or physical approaches. In this Review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications, thus bringing together low-dimensional and bulk materials for thermoelectric applications. Particular emphasis is given in this Review to the ability to achieve 1) a simultaneous increase in the power factor and a decrease in the thermal conductivity in the same nanocomposite sample and for transport in the same direction and 2) lower values of the thermal conductivity in these nanocomposites as compared to alloy samples of the same chemical composition. The outlook for future research directions for nanocomposite thermoelectric materials is also discussed.
3,562 citations
TL;DR: A successful implementation through the use of the thallium impurity levels in lead telluride (PbTe) is reported, which results in a doubling of zT in p-type PbTe to above 1.5 at 773 kelvin.
Abstract: The efficiency of thermoelectric energy converters is limited by the material thermoelectric figure of merit (zT). The recent advances in zT based on nanostructures limiting the phonon heat conduction is nearing a fundamental limit: The thermal conductivity cannot be reduced below the amorphous limit. We explored enhancing the Seebeck coefficient through a distortion of the electronic density of states and report a successful implementation through the use of the thallium impurity levels in lead telluride (PbTe). Such band structure engineering results in a doubling of zT in p-type PbTe to above 1.5 at 773 kelvin. Use of this new physical principle in conjunction with nanostructuring to lower the thermal conductivity could further enhance zT and enable more widespread use of thermoelectric systems.
3,401 citations